1. Field of the Invention
The present invention relates generally to a hand-held information processing apparatus which, upon connection with an external power source by way of, e.g., an AC adapter, supplies an electric power from an external power source to a load and charge an internal battery, and to a charging apparatus and method for the information processing apparatus. More particularly, the invention relates to a hand-held information processing apparatus for preventing degradation of the battery upon the use with the external power source being connected, as well as to a charging apparatus and method for the information processing apparatus.
2. Description of the Related Arts
With recent progress toward miniaturization of elements, high integration of LSIs and high performances of CPUs with enriched communication facilities such as cellular phones, personal computer communications and internets, markets for hand-held equipment such as notebook-sized personal computers, handy terminals, mobile computers, etc., are expanding. Use of a lithium ion battery (L+ battery) as the battery for such hand-held equipment is rapidly prevailing of late. The lithium ion battery has a weight energy density about three times and a volume energy density about twice the nickel-cadmium hydrogen battery. The lithium ion battery is a small-sized and lightweight high-capacity battery and is used for various hand-held equipment. The lithium ion battery includes, as its basic unit, battery cells generating nominal voltage of 3.6 volts and has a tubular or rectangular package for housing a corresponding number of cells to the power-supply voltage required by the hand-held terminals. For example, two cells and three cells correspond to 7.2 volts and 10.8 volts, respectively. The mode of charging the lithium ion battery loaded in the hand-held equipment such as the notebook-sized personal computers needs to be constant-voltage constant-current charge. In such battery charge, the quantity of charge is determined depending on the charging voltage, charging current and charging time. In case of the hand-held equipment such as the notebook-sized personal computers, the battery operating time becomes longer accordingly as the quantity of charge of the lithium ion battery, i.e., the capacity upon the full charge is larger. For this reason, the charging is made at as a high voltage as possible within a permissible range so as to secure a larger capacity upon the full charge. It is further necessary to set as a final discharge voltage a minimum voltage value ensuring a stable operation of the equipment, but the apparatus operation time may vary depending on the manner of setting the final discharge voltage. On the other hand, the lithium ion battery has degradation properties that its capacity lowers in the same manner as the case of the charge and discharge merely by being left to stand under the high-temperature environment in charged state. The degree of degradation depends on the temperature when it is left to stand and on the charging voltage, so that the degradation is faster accordingly as the temperature is higher. The notebook-sized personal computer may be used on the desk with the AC adapter connected at all time without being limited to the hand-held use. In this case, the notebook-sized personal computer is constantly powered from the AC adapter and is by no means powered by the internal battery. However, considering the abnormalities such as the short break, instantaneous stop and service interruption into consideration irrespective of the constant supply of power for the notebook-sized personal computer from the AC adapter, it is not preferable that the battery charge capacity is null. Furthermore, in the event that the hand-held use is suddenly desired in spite of the frequent desk-top use, the empty battery will not permit the hand-held use till the termination of the battery charging. In this manner, the charging capacity of the internal battery must be kept at the full charged state in proximity to 100% even in the cases where the notebook-sized personal computer is always used on top of the desk with the AC adapter connected.
Normally, upon the operation with the AC adapter connected, there is no supply of power from the internal battery to the apparatus, so that when the internal battery is once charged, the charging capacity will remain near-full charged close to 100% with no need for recharging. However, without limitation to the lithium ion battery, the secondary batteries may suffer a gradually decreasing charging capacity due to the internal leak even in its full-charged state. This is called self-discharge. Thus, even in the event that the apparatus such as the notebook-sized personal computer is operated with the AC adapter connected, it is necessary to make recharging to supplement the self-reduction of the charging capacity attributable to the self-discharge of the internal battery. In the case of Nicad battery or NiMH battery, a common method is the trickle charging in which the quantity equal to the self-discharge continues to be charged at all times. On the other hand, due to the presence of a risk that the battery may be damaged by the continuing trickle charging, the remaining quantity of the battery is monitored so that the charging is effected when the remainder has reduced to a certain degree, to thereby supplement the quantity of self-discharge. For this reason, the desk-top use of the notebook-sized personal computer with the AC adapter connected at all times allows the power to be supplied from the AC adapter to the load, so that although there is no discharge from the lithium ion battery, the lithium ion battery is always put in the full charged state, which may cause any degradation without charge and discharge for the load. Such a problem occurs similarly irrespective of its significance in not only the lithium ion battery but also in the other secondary battery such as lithium polymer battery. Raised charging voltage of the lithium ion secondary battery will increase the charging capacity and elongate the battery-based operating time of the notebook-sized personal computer in the hand-held use, whereas the raised charging voltage may cause the same degradation as the case of charge and discharge of the battery even in the cases where the battery is not discharged in the AC adapter-based operation. A prompt approach to solution of degradation of the battery in the high-temperature environment is to lower the charging voltage. The lowered battery charging voltage can prevent the degradation of the battery in the high-temperature environment, but may shorten the battery-based operating time of the notebook-sized personal computer due to the reduced quantity of battery charge.
According to the present invention there are provided a hand-held information processing apparatus, a charging apparatus and a charging method wherein when the apparatus such as a personal computer is in hand-held use, the charging voltage of the battery is raised to increase the charging capacity so that the battery operating time is maximized, whereas when the apparatus such as the personal computer is in desk-top use with the AC adapter connected at all times, the charging voltage of the battery is lowered to thereby prevent any degradation of the battery in high-temperature environment.
Identification of whether the apparatus such as the personal computer is in hand-held use or desk-top use can be made by identifying the trigger phenomenon upon the start of the charging of the battery incorporated in the apparatus. When the apparatus such as the personal computer is in desk-top use, the AC adapter remains connected at all times. In this case, the charging is mainly directed to replenishment of the self-discharge of the internal battery. On the other hand, the hand-held use often causes the battery-based apparatus operation. For this reason, charging of the internal battery is performed when the AC adapter is mounted on the apparatus or when the internal battery is loaded in the apparatus with the AD adapter being connected to the apparatus. In this manner, the mode of operation of the apparatus can be recognized in a corresponding manner to the trigger phenomenon to start the charge of the internal battery. Thus, the present invention provides a hand-held information processing apparatus, a charging apparatus and a charging method which realize both the prevention of degradation of the battery in the desk-top use with the AC adapter being connected at all times and the securement of the battery charging capacity in the hand-held use.
According to first and second aspects of the present invention there are provided a hand-held information processing apparatus and a charging apparatus which, when an external power source is unconnected for example, supply an electric power from an internal battery to a load and which, upon connection with the external power source, supplies an electric power from the external power source to the load and charges the internal battery, the apparatuses each comprising a charging circuit capable of charging the battery by setting different charging voltages; and a charging control unit which variably sets the charging voltage of the internal battery in response to trigger phenomenon to start charging of the internal battery. Thus, in the present invention, the charging voltage is raised to effect the charging as much as possible in the charge upon the detection of connection with the AC adapter and upon the detection of loading of the battery, whereas the charging voltage is lowered in the charge for supplementing the reduction attributable to the self-discharge, to thereby suppress the occurrence of the charge/discharge cycle arising from the self-discharge of the lithium ion battery to consequently prevent the degradation of the battery and elongate the service life thereof.
In this event, correspondingly to the trigger phenomenon to start charging of the internal battery, the charging control unit sets either a first charging voltage at which the charging capacity of the internal battery is maximized or a second charging voltage which is lower than the first charging voltage. When starting charging of the internal battery as a result of connection with the external power source, the charging control unit sets the first charging voltage for charging at which the charging capacity of the internal battery is maximized, and wherein when starting charging as a result of recognition of a reduction in the capacity of the internal battery due to its self-discharge, the charging control unit sets the second charging voltage which is lower than the first charging voltage. With the external power source connected, when starting charging of the battery as a result of mounting of the internal battery on the apparatus, the charging control unit sets the first charging voltage at which the charging capacity of the internal voltage is maximized, and wherein with the external power source connected, when starting charging as a result of recognition of a reduction in the capacity of the internal battery due to its self-discharge, the charging control unit sets the second charging voltage which is lower than the first charging voltage. The apparatuses may each further comprise a setting change unit which changes set voltages as charging voltages to be set for the charging circuit to any voltages, the set voltages being defined for each trigger phenomena to start charging of the internal battery. As to the lithium ion battery, the setting change unit sets for the charging circuit the first charging voltage of 4.2V per cell and the second charging voltage of 4.1V per cell for example. The apparatuses may each further comprise a switching operation unit by means of which, for the charging circuit, the user switches the charging voltage to either the first charging voltage or the second charging voltage. This enables the selection of the charging voltage to be made by the judgment of the user. For instance, upon the hand-held use with the AC adapter removed, the user may change the setting of the charging voltage to a higher voltage previous to the removal of the AC adapter, whereby the user can shift to the hand-held use after maximizing the charge.
According to a third aspect of the present invention there is provided a method of charging equipment which, when an external power source is unconnected, supplies an electric power from an internal battery to a load and which, upon connection with the external power source, supplies an electric power from the external power source to the load and charges the internal battery, the method comprising the step of changing the charging voltage of said internal battery in response to trigger phenomenon to start charging of the internal battery, to charge said internal battery. More specifically, the method may further comprise the step of, in response to trigger phenomenon to start the charging of the internal battery, setting either a first charging voltage at which the charging capacity of the internal battery is maximized or a second charging voltage which is lower than the first charging voltage, to charge the internal battery. The details of this charging method are substantially the same as the case of the apparatus configuration.
The above and other objects, aspects, features and advantages of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings.